1. Field of the Invention
The present invention relates to a liquid discharge head that discharges liquid by the utilization of bubbles generated by heating liquid in flow paths for bubbling. The invention also relates to a recording apparatus that uses the liquid discharge head for recording information, such as images, characters, on a recording sheet, film, or some other recording medium.
Conventionally, the liquid discharge head is used for the application thereof in various fields, such as micro processing, experiment and analysis, image formation, among some others. Here, however, the description is made of the head of ink jet recording method as the example.
2. Related Background Art
The ink jet recording method, in which ink droplets are discharged for the adhesion thereof to a recording medium for recording images and the like, makes high-speed recording possible with the advantage that it performs recording in high quality with less noise. Further, the ink jet recording method makes it easier to record images in colors, and among many other excellent advantages, it can record on ordinary paper, and the like. Furthermore, the entire body of the apparatus can be made compact easily.
A recording apparatus that adopts the ink jet recording method of the kind is generally provided with a recoding head having discharge ports for enabling ink to fly for discharging it as ink droplets; ink flow paths communicated with the discharge ports; energy generating means arranged for a part of each ink flow path to give ink discharge energy for discharging it. Here, for example, there have been disclosed in the specifications of Japanese Patent Publication 61-59911, Japanese Patent Publication 61-59912, Japanese Patent Publication 61-59913, and Japanese Patent Publication 61-59914, respectively, a method for discharging ink by use of electrothermal converting element as energy generating means to enable thermal energy, which is generated by the application of electric pulses, to act upon ink.
The recording method disclosed in each of the aforesaid publications is such that a bubble is generated in ink with the action of thermal energy given to the ink, and by the force exerted by the action brought about by the abrupt expansion of such bubble, ink is discharged from each discharge port provided for the leading end of the recording head, and then, images are formed by the adhesion of the ink droplets discharged to a recording medium. In accordance with this method, it is possible to arrange discharge ports of the recording head in high density so that images can be recorded at high speed in high resolution and high quality. The recording apparatus that uses this method is therefore adoptable as information output means for a copying machine, a printer, facsimile equipment, and others.
For the ink jet recording method, the electrothermal converting element that has been described above should be provided, that is, it is necessary to provide a heat-generating member for heating liquid. Then, for the conventional ink jet recording method, there has been adopted a structure in which a thin resistive film is provided for the wall faces of the flow path, and electrodes are electrically connected to the two sides of the thin resistive film for the application of electric pulses.
However, when the thin resistive film is provided for the wall faces as described above, the thermal energy that has been generated by the thin resistive film is scattered and lost on the wall faces in a considerable proportion. As a result, efficiency is lowered in converting thermal energy into energy for bubbling use (bubbling energy), and in some cases, power dissipation becomes greater. In order to solve a problem of the kind, there has been disclosed in the specifications of Japanese Patent Application Laid-open No. 55-57477 and Japanese Patent Application Laid-open No. 62-94347 a liquid discharge head capable of reducing power dissipation by use of a heat-generating member that extends into the interior of each flow path, thereby to prevent heat from being scattered and lost in the recording head main body or the base plate thereof so as to effectuate the effective conversion of electric energy supplied to the heat-generating member into the bubbling energy.
However, the conventional liquid discharge head, which is structured to improve the efficiency of conversion of the supplied electric energy into bubbling energy by use of the heat-generating member that extends into the interior of the flow path as described above, makes it difficult to cause the heat of the heat-generating member to be diffused in the base plate. Therefore, it takes time to reduce the temperature of the heat-generating member after bubbling, and there exists a drawback that more time is required before transition to the next heating and bubbling can be made. Under the circumstances, it is difficult for the conventional liquid discharge head to repeat liquid discharges at high frequency.
Also, likewise, since the conventional liquid discharge head is structured so as to make it difficult for the heat of the heat-generating member to be diffused in the base plate, there is a drawback that the surface temperature of the heat-generating member cannot be reduced sufficiently by the time the bubble generated in the liquid is made extinct (hereinafter referred to as the time of bubble extinction). Thus, there is a fear that liquid is heated even after bubble extinction, thus generating a bubble again.
Further, if the phenomenon that the liquid is again heated after bubble extinction so that a bubble is generated again (hereinafter referred to as re-boiling phenomenon) should take place, the number of cavitation shocks given to the surface of the heat-generating member is increased. Thus, there is a fear that the durability of the heat-generating member deteriorates.
Also, when the re-boiling phenomenon occurs, it increases the refilling time, which is the time required for filling the flow path with liquid to be used for discharge prior to bubbling. This makes it difficult to repeat liquid discharges at high frequency.
Now, the present invention is designed with a view to solving the problems discussed above. It is an object of the invention to provide a liquid discharge head capable of suppressing the increase in time required for making the transition to the subsequent heating and bubbling for the heat-generating member, which is supported in a state of having gaps from both sides of the inner wall faces of a bubbling chamber, while preventing the occurrence of re-boiling phenomenon and making the power dissipation thereof smaller, and also, to provide a recording apparatus provided with such liquid discharge head.
In order to achieve the aforesaid object, the liquid discharge head of the present invention is a liquid discharge head for discharging a liquid droplet utilizing a generated bubble by heating liquid to bubbling, which comprises a discharge port for discharging a liquid droplet; a bubbling chamber communicated with the discharge port for filling liquid; a heat-generating member arranged in the bubbling chamber, being supported in a state of having gaps on both sides from the inner wall faces of the bubbling chamber, and a supporting portion for supporting the heat-generating member. Then, for this liquid discharge head, after bubble generation in the liquid by the heat-generating member, the surface temperature of the heat-generating member is made lower than the bubbling temperature at the time of bubble extinction, by heat radiation from the heat-generating member to the supporting portion side.
With the liquid discharge head of the invention thus structured, heat is radiated from the heat-generating member to the supporting portion side subsequent to having liquid bubbled and discharged by the heat-generating member. Thus, the surface temperature of the heat-generating member is made lower than the bubbling temperature at the time of bubble extinction, and the reboiling phenomenon at the time of bubble extinction is suppressed. Also, the liquid discharge head is arranged so that the heat-generating member is supported in a state of having gaps on both sides from the inner wall faces of the bubbling chamber where liquid is filled. In this way, it is made possible to prevent heat from being diffused in the base that supports the liquid discharge head and in the head supporting portion side. The electric energy supplied to the heat-generating member is converted into bubbling energy efficiently. In this respect, as for the structure that supports the heat-generating member, so long as the structure can support it without closing off the discharge port, it may be possible to support the heat-generating member either in a twin-beam fashion or in a single-beam (cantilever) fashion.
Also, the liquid discharge head of the present invention is formed to be flat by a thin resistive film, and first and second electrodes for applying an electric signal to the heat-generating member are provided in positions facing each other with the heat-generating member between them, and the heat-generating member bubbles liquid in the vicinity of both faces thereof, respectively.
As described above, the liquid discharge head of the present invention generates a bubble on both faces of the flat heat-generating member. Thus, as compared with the conventional heat-generating member, which is installed on the inner wall face of the liquid discharge head, the volume of bubble is made approximately twice as large, and the discharge energy of the liquid is enhanced accordingly. Also, in accordance with the liquid discharge head of the present invention, it becomes possible to obtain the same amount of discharge energy with a lesser amount of power dissipation as compared with the conventional liquid discharge head. In this respect, the shape of the heat-generating member may be one other than a flat shape.
Also, when a flat heat-generating member is used, only the heat-generating member is heated abruptly up to a temperature at which film boiling occurs in order to generate bubbles at the same time on both faces of the heat-generating member, respectively, for example. Thus, the temperature of the heat-generating member rises more than the bubbling temperature evenly in a short period of time. Therefore, variation in the bubbling times on the two faces of the heat-generating member is reduced, and bubbles can be generated simultaneously on both faces of the heat-generating member.
Also, for the liquid discharge head of the present invention, the supporting portion is provided with the first and second electrodes, and if the distance between the first electrode and the second electrode is W1, the heat conduction distance of the heat-generating member at the time of bubbling is d1, and the heat conduction distance of the heat-generating member at the time of bubble extinction is d2, then the distance W1 satisfies the condition: 2d1 less than W1 less than d2. In this manner, it becomes possible to make the surface temperature at the time of bubble extinction lower than the bubbling temperature, because the heat that may escape to the supporting portion side is made smaller at the time of bubbling.
Also, it is preferable for the liquid discharge head of the present invention that the liquid contains water, and the surface temperature of the heat-generating member is made 300xc2x0 C. or less at the time of bubble extinction by heat radiation from the supporting portion. In this respect, it is more preferable that the surface temperature of the heat-generating member is made 100xc2x0 C. or less at the time of bubble extinction.
Also, the liquid discharge head of the present invention is formed to be a thin film-laminated element having protection films laminated on both sides of the thin resistive film, and if the thickness D of the thin film-laminated element is larger than the value of 2d1 in the previous condition, the ratio of thermal energy that may escape to the supporting portion side is increased at the time of bubbling. As a result, the thermal energy that is converted into bubbling energy is made significantly small. This is not preferable. Therefore, D less than 2d1 should preferably be satisfied. However, if the thickness D is extremely small, the strength of beam portion is lowered. This is not preferable, either. Typically, therefore, in consideration of such requirements as pulse width, material of the thin film-laminated layer, and volume of the liquid droplet, the thickness D of the thin film-laminated layer element should preferably be 0.1 xcexcm or more and 12 xcexcm or less, and more preferably, 0.5 xcexcm or more and 3 xcexcm or less, with respect to the aforesaid condition of the thickness D.
Also, the liquid discharge head of the present invention is provided with the heat-generating member having a bubbling region of an area S1 on the front and rear sides, respectively; the front-rear communication path having a minimum aperture area S2 to enable each bubbling surface on the front and rear sides of the heat-generating member to be communicated with each other; the ink supply port having a minimum aperture area S3; and the discharge port having a minimum aperture area S4, and it is preferable to make arrangements so that the conditions of S2 greater than S3, S2 greater than S4, and S1 greater than S4 are satisfied, respectively. In this way, it becomes possible to enable bubbling on the rear and front faces of the heat-generating member to contribute effectively to discharging ink droplets, and also, to enhance the utilization efficiency of energy for the nozzles as a whole.